Neglected tropical diseases

Chagas disease (American trypanosomiasis)

Carlos Ribeiro Justiniano Chagas in his laboratory (1879-1934)
©Oswaldo Cruz House - Fiocruz

Chagas disease is a zoonosis (or an anthropozoonosis) due to the flagellated protozoan parasite Trypanosoma cruzi. It is transmitted to man by infected faeces of a blood-sucking triatomine bug through the insect sting, another skin break or through mucous membranes, including conjunctiva or oral/digestive mucosa, occasionally causing outbreaks with contaminated food. Transmission through blood transfusion, pregnancy and delivery are also possible, and less frequently, through organ transplantation or laboratory accident.


Clinical signs

The acute phase, with high parasitaemia, commonly lasts around two months. Most of the cases are a- or oligosymptomatic, but depending on the inoculation site, the first sign can be a skin chancre (chagoma) or unilateral purplish orbital oedema (Romaña sign) with local lymphoadenopathies and fever over several weeks. That can be accompanied, among others, by headache, pallor, myalgia, dyspnoea, oedema in inferior limbs or face, abdominal pain, cough, hepatomegaly, rash, painful nodules, splenomegaly, generalized oedema, diarrhoea, multiple lymphoadenopathies, myocarditis (chest pain, heart failure) and more rarely meningoencephalitis (seizures, paralysis). Morbidity can be higher in children under five, elderly, immunocompromised or in cases with possible high parasite inoculum, such as seen in oral outbreaks. In AIDS the meningoencephalitis is the more frequent manifestation (differential diagnosis with toxoplasmosis).

The chronic phase, with parasites hidden in target tissues - especially heart and digestive smooth muscle, has different possible clinical forms: a) asymptomatic (indeterminate form), more frequent, typically in the beginning of the chronic phase and lasting all life in most of the patients; b) cardiac form, till 30% of the patients, with conduction disorders, arrhythmia, cardiomyopathy, heart failure and secondary thromboembolism; c) digestive lesions (megaoesophagus and megacolon) or mixed forms (cardiac plus digestive), till 10% of the patients, just seen south to the Amazon basin.

Laboratory diagnosis

Four Trypanosoma cruzi in blood sample
© J.R.Coura, Oswaldo Cruz Institute - Fiocruz

In the acute phase (or in reactivation for immunosuppression) a blood wet smear or a blood concentration technique such as microhaematocrit or Strout technique, must be used. Stained preparations, such as malaria films, detect parasites when parasitaemia is high (acute phase). In the Amazon basin microscospy technicians of malaria have been trained to detect acute individual cases and through them possible oral outbreaks and areas of active transmission (surveillance system). In the chronic phase serologic tests should be used: the detection of anti-Trypanosoma cruzi antibodies through a conventional or recombinant enzyme-linked immunosorbent assay (ELISA), indirect hemagglutination assay, indirect immunofluorescence assay, western blot, rapid diagnostic test (such as immunochromatography), among others. Especially for research purposes, haemoculture, xenodiagnosis (faeces examination of uninfected triatomine bug fed with the patient's blood) and Polymerase Chain Reaction (PCR) are also used.

Prevention

There is not any available vaccine. Depending on the region, key tools are vector control (insecticide spraying), house improvement (such as plastered walls, cement floors, corrugated-iron roofs) and personal preventive measures (such as bed nets) and good hygiene practices in food preparation, transportation, storage and consumption bed nets), together with the transmission control through blood transfusion and organ transplantation. Secondary prevention is important in: congenital transmission - diagnosis of infected pregnant women and detection of possible newborn infection with parasitological or serological tests after eight months of age (with no longer existing mother antibodies); laboratory accident prevention using safety standard protocols (laboratory coat, gloves, face mask, cap, glasses), especially when dealing with trypomastigotes - the human infective form of the parasite.

Treatment

The etiological treatment is urgently indicated in the acute phase and reactivation (immunosuppression). At that moment parasitological cure rates are almost 100% and they decrease with longer duration of the infection/disease. At younger age the prevalence of side-effects is also lower. The etiological treatment is indicated, as well, in congenital infection and early chronic phase. In adults, especially those with indeterminated form, etiological treatment should be offered, but balancing potential benefits (to prevent or delay the development of the Chagas disease) against a long treatment schedule together with frequent side-effects.

The two available drugs are benznidazole and nifurtimox. Main contra-indications are pregnancy and renal or hepatic failure. Especially with nifurtimox, also psychiatric or neuronal disorders (such as seizures).


Nifurtimox is free of charge through WHO-Bayer agreement. For ordering, please contact Albajar Vinas P. Tel.:+41-22-7911261; albajarvinasp@who.int

Benznidazol is produced by Laboratório Farmacêutico do Estado de Pernambuco (LAFEPE). For ordering, please contact LAFEPE, Largo de Dois Irmãos 1117 - Dois Irmãos. 52171-010 - Recife - PE, Brazil. Tel.: +55-81-31831100; sac@lafepe.pe.gov.br

Share